Dangers Associated With a Forgotten Appliance: Water Heaters (Part II)

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By Thomas J. Wuori, JD


In the Spring 2003 issue of Burn Support News, we looked at the flammable vapor ignition hazard associated with hot water heaters.1 In this article, we look at scalds, another hazard presented by hot water heating systems and of most significance to the young, the elderly, and the disabled.

According to the National Safe Kids Coalition and the Consumer Products Safety Commission, 4,000 to 5,000 children are scalded annually. A significant number of the elderly are also scalded every year. Why? In many instances, because the hot water heating system has been allowed to produce and distribute hot water at temperatures in excess of 120oF at the point of use: showerheads, tub faucets, and sink faucets.

In many cases, the thermostats on the water heaters are set at temperatures well in excess of 120oF. Most importantly, and usually contrary to local code requirements, proper “anti-scald” or temperaturelimiting devices have not been installed at either the “point of use” (showerhead and faucet) or “point of source” (near the water heater) to prevent these excess temperatures from ever coming out of the shower head or faucets.


The circumstances in which people are scalded every year vary, but many of the patterns are similar. The following are fact patterns from actual cases:

  • A 10-year-old girl decides to help her mother give her little brother a bath. Unfortunately, she does not understand the shower valve and only turns on the hot water. While the tub fills, her little brother runs into the bathroom and excitedly jumps into the tub. The water is well in excess of 150oF, and he receives second- and third-degree burns over his feet and legs and splash burns on other portions of his body.
  • An elderly person is comfortably taking a shower at a senior living facility when the water suddenly fluctuates and spikes to a scalding temperature. After unsuccessfully trying to manipulate the shower valve, he pulls the shower curtain in front of him and tries to escape. Within seconds he receives second- and third-degree burns over his legs and feet. Eventually, he dies after a month at a trauma burn hospital.
  • A disabled woman is comfortably taking a shower in her apartment when the temperature spikes after she had begun bathing. By the time she is able to escape from the tub she is severely burned on portions of her chest, arm, and back.

It is not just the temperature of the hot water that is important, but also the time-temperature relationship. As shown in the diagram, the time to achieve a serious burn injury decreases exponentially with each increasing degree of hot water above 120oF:

For example, you can have a third-degree burn injury in 1 second at 156oF, 5 seconds at 140oF, but it will take upwards of 10 minutes to achieve such a burn at 120oF—and hours at 110oF. The human tolerance for pain is less than 118oF, so a shower with 120o water will hurt, but you would need to be exposed to that water constantly for upwards of 8 minutes to get even a first-degree burn. It is unlikely that anyone would stay exposed to this painful water for minutes. Thus, the need to have hot water delivered at no greater temperature than 120oF is critical—and one can still take a “hot shower” without a significant risk of a scald.


Scalding water burns people because (1) there are no mechanical devices used in the hot water heating system to limit the temperature (or they are present but not installed or maintained properly) and (2) the thermostat is set too high. Merely setting the thermostats on a water heater at 120oF or less does not guarantee that in all circumstances the water will never come out higher than 120oF. In fact, many codes even mandate that you cannot achieve the 120oF maximum temperature by the thermostat. For example, the International Plumbing Code, Section 424.4 (1997) states, “…The water heater thermostat shall not be used as the temperature control device for compliance [with the 120oF requirement].” Instead, temperaturelimiting devices must be used either at the point of source or the point of use (preferably both).3 There are reasons why setting the thermostat at 120oF is not enough, is criticized by some professionals, and is prohibited by some codes as the method to limit temperatures. Generally, hot water heaters, by design, control the temperature with a thermostat. Each thermostat, however, may have a variance of ±10 degrees from that of its setting. Thus, if the thermostat is set at 120oF, in some circumstances you can achieve hot water that reaches upwards of 130oF. In addition, by design, the hot water heaters have burners at the bottom that heat the water when there is a demand for it. Like hot air, hotter water rises. Thus, there can be a stratification or layering effect when this hot water rises, depending upon usage and consumption. Some water heater manufacturers in their literature even indicate that this layering or laminar effect can produce results that vary ±30 degrees. Thus, even a setting of 120oF on a water heater may produce hot water temperatures upwards of 160oF (30o variation due to the layering effect plus the 10o variance from the thermostat setting). That is why only setting the thermostat at 120oF, while safer than a higher setting, does not in and of itself guarantee that a scald injury cannot or will not occur. And a setting higher than 120oF without any temperature-limiting device is more dangerous.

Setting the thermostat at 120oF, with or without temperature-limiting devices, has also been criticized by some plumbing professionals as ignoring hazards presented by Legionella pneumophila, the inhalation of which while showering can cause Legionnaires’ disease. The literature suggests that the bacteria breed best around 70–120oF within biofilms and in stagnant water (dead-end piping, for example). Thus, some in the plumbing trade recommend that a thermostat setting or storage of the hot water at 135–140oF can address that hazard, while proper thermostatic mixing valves can address the scald hazard. [See, for example, American Society of Plumbing Engineers, Board of Directors Position Statement (135–140oF storage recommenda-tion); OSHA Technical Manual, Section III: Chapter 7 (domestic hot water stored at minimum of 140oF and delivered at 122oF (referring to workplace and not residential settings)].


Mechanical devices can prevent scalding temperatures from ever coming out of a showerhead or faucet. Tempering/mixing valves should be installed as part of the piping system near the water heater and can be set so that temperatures above 120oF never arrive at the point of use (showerhead and faucet).

In addition, you can install various types of “antiscald” devices at the point of use (as part of the bathroom piping, showerhead, faucet, etc.). In the event of a failure of either, having point-of-source and point-of-use devices is always safer. (Literature from Watts Regulator Company, for example, states that a point-of-source device meeting ASSE 1017 standards should be used in combination with an ASSE 1016 point-of-use device.)

By setting the hot water heater thermostats lower and installing anti-scald devices at both the point of source and point of use, scald injuries can be prevented in residential-type settings. Proper installation and continuing maintenance and repair of these valves then becomes critical for short-term, as well as longterm, effectiveness. These temperature-limiting devices need to be sized properly and installed by a qualified professional. In addition, other devices, such as check valves, may be required to prevent uncontrolled hotter water in kitchen piping from escaping into the main water system.

Legal claims have been brought against the building owners, maintenance contractors, plumbing contractors, and others for scald injuries. In many of these circumstances, the thermostat was set well above 120oF and the residence or the apartment complex had no anti-scald devices at either the point of source or point of use, despite code requirements for them. In some cases, anti-scald device(s) existed, but were either installed improperly or not properly maintained such that scalding water was still able to reach tenants and cause significant burn injuries.


Existing laws in most states throughout the country address the scald hazard. For example, most building and plumbing codes contain requirements that (a) the delivered water be 120oF or less, and (b) the building owner does so by installing and maintaining thermostatic mixing devices at the point of source or use. Many jurisdictions have adopted and incorporated recognized codes that require delivered water to be 120oF or less:

These codes provide adequate laws to address the hazard if followed and enforced. However, in some cases the building owners and/or plumbers or contractors do not obtain legally required permits so that supervision and inspections of plumbing work can occur.

In response to some claims that older buildings are “grandfathered” and do not have to comply with the most recent standards, most codes have provisions by which the code official can require thermostatic mixing devices to be installed. Without temperaturecontrol devices, there is clearly a “hazard to life, health or property … created by such plumbing system.” See Section 102.2, International Plumbing Code (1995). In addition, many codes have sections pursuant to which safety devices can be required even if not specifically required by other code sections. See, for example, Section 102.9, Requirements not covered by code. (Code official can determine requirements for public safety, health and general welfare.)

Given the continuing scald injuries, much remains to be done. The standard safety hierarchy is: (1) design out the hazard, (2) guard against it, and (3) warn about it. A properly designed hot water heating system, required by most current codes, can prevent scalds even if there are the inevitable human mistakes (for example, not watching a child in the tub). One prevention strategy for burn units and support groups may be to work with your local code officials to obtain better enforcement, interpretation, or adoption of these code provisions.

Follow these important guidelines to prevent scalds:

  • Find out if the system providing you with hot water has anti-scald, temperature control devices (if not, why not).
  • In apartment complexes, nursing homes, assisted living facilities, ask the landlord about, and look at, any temperature-control devices.
  • Use a master mixing valve (ASSE 1017 approved), point-of-use temperature control device (ASSE 1016 approved) on shower valves, and maximum temperature limit stops on faucets and shower valves. Anti-scald devices in bathtub faucets, showerheads, or as part of the piping system are effective in preventing water temperatures higher than 120oF from reaching you. Some new devices shut off the flow of water to a faucet or shower when the water temperature exceeds 120oF.
  • Set your water heater thermostat to a safe temperature.
  • Make sure that plumbing work has been and is done (a) through the local code official with all necessary permits and inspections, and (b) by a licensed plumber.
  • Test the water temperatures (use an inexpensive candy thermometer).
  • Make sure maintenance is done on hot water heating systems.
  • Never leave a child alone while drawing the water or bathing.
  • Test the water before bathing; note, however, that without temperature-control devices water can spike or fluctuate to scalding temperatures even though the temperature initially was fine.

Learn about your hot water delivery system today.


Thomas Wuori is a partner with the law firm of Halpert, Weston, Wuori & Sawusch, PC. For more than 10 years, Mr. Wuori has been representing burn survivors of scalds, flammable vapor ignitions, propane explosions, chemical accidents, and car accidents. 


This story is an excerpt from The Phoenix Society’s® Burn Support News, Fall Edition 2003. Burn Support News is a quarterly publication that contains articles on the emotional, psychological, and social aspects of burn recovery.  All Rights Reserved.
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